Asynchronous Transfer Mode (ATM) ATM Quick Highlights. The B-ISDN ATM Reference Model. ATM History

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Chart © Glenn W Cox, 2001-2004

Asynchronous Transfer Mode (ATM)

• Background

• Physical and ATM Layers

• AALs

• Applications

ATM - Background

ATM Quick Highlights

• The Telecom Industry’s thrust into multi-media data

networking

• Comm unit is small, fixed-sized “cell” (53 bytes)

• Built to provide Quality-of-service

• Connection-oriented

• Designed to run over SONET/SDH

ATM - Background

ATM History

1980 ISDN

1985 B-ISDN Study Group ITU chooses ATM approach B-ISDN

53-byte cell chosen 1990

ATM Forum founded

1995

Anchorage Accord Stabilizes Specifications

2000

ATM - Background

Upper Layers Upper Layers Control Plane User Plane

Management Plane Management Plane

ATM Adaptation Layer (AAL)

Physical Layer Convergence Sublayer Segmentation and Reassembly Sublayer Transmission Convergence Sublayer (Framing) Physical Medium Dependent Sublayer CS SAR TC PMD ATM Layer

The B-ISDN ATM

Reference Model

Physical Medium Cells, VC’s Packets User and Control Data Transfer Layer Management

Plane Management

ATM - Background

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Why?

• Why a small cell instead of a large packet?

• Queue delays tend to grow as packet size grows. A

small cell helps maintain streamlined flows.

• No/little performance loss due to padding large fields

• Small cells better for voice

• No need for in-route fragmentation

ATM - Background

Why?

• Why a fixed cell size instead of variable-size

packets?

• Switch architecture can be optimized to the fixed

size, so switching can be done in hardware

• Scalable parallel switch designs

ATM - Background

Why?

• Why 53 bytes?

– US wanted 64 payload bytes, Europe wanted 32

– Compromised on 48

– +5 header = 53

ATM - Background

Why?

• Why start out with 9% Overhead?

Overhead isn’t everything…

ATM - Background

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ATM + and –

+

• QoS

• Multimedia Support

• Hardware Switching -> High Speed

• Connection-Oriented (-?)

-• IP Support

• LAN arena dominated by huge installed Ethernet base

• Ethernet growing toward MAN, WAN

• Connection-Oriented (+?)

• Living up to the hype of the early 90’s

ATM - Background

Chart © Glenn W Cox, 2001-2004 53-Byte Cells 53-Byte Cells

ATM Architecture

Physical Layer ATM Layer Physical Layer User Application Da ta Vo ic e Vi de o ATM Layer Physical Layer End Station Switch User Application Da ta Vo ic e Vi de o ATM Adaptation Layer (AAL) ATM Layer Physical Layer End Station ATM - Background ATM Adaptation Layer (AAL)

ATM

• Background

• Physical and ATM Layers

• Cells, Formats, and Addressing

• Virtual Circuits

• Switches and Media

• Interfaces

• AALs

• Applications

ATM

- Physical and ATM Layers

Cell Format

Header Payload

5 Bytes 48 Bytes

GFC VPI VCI PTI

C L P HEC UNI Header

GFC VPI VCI PTI

C L P HEC NNI Header ATM

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Header Error

Control (HEC)

bbbbbbbbbbbbbbbbbb bbbbbbbbbbbbbbbbbb

First Four Cell Header Bytes

/

x8+ x2+ x + 1 Remainder + 01010101

HEC

If P(bit error) = 10-8, then P(Undetected header error) = ~10-20: at OC-3, about 1 per 90,000 yrs

HEC covers the header only, not the payload -- the goal is to ensure correct delivery

HEC also assists in synchronizing:

- Look at 53-byte sequences until you find one where the HEC field works correctly - If this holds up for D sequences in a row, assume you’ve synched

- p(bad synch) = ~2-8D

ATM

UNI Header Fields

GFC VPI VCI PTI

C L P

HEC

GFC - General Flow Control

Only used between host and network. Overwritten by first switch. VPI - Virtual Path ID

VCI - Virtual Circuit ID PTI - Payload type ID

CLP - Cell Priority (ID’s cells for deletion when congestion experienced) HEC - Header Checksum (all 1-bit errors corrected, 90% of multi-bit errors

detected) ATM

NNI Header Fields

GFC VPI VCI PTI

C L P

HEC

VPI - Virtual Path ID VCI - Virtual Circuit ID PTI - Payload type ID

CLP - Cell Priority (used to ID cells for deletion when congestion experienced) HEC - Header Checksum (all 1-bit errors corrected, 90% of multi-bit errors

detected) ATM

PTI Field Codes

000 User Data Cell Type 0 No congestion experienced 001 User Data Cell Type 1 No congestion experienced 010 User Data Cell Type 0 Congestion experienced 011 User Data Cell Type 1 Congestion experienced 100 Maintenance info between adjacent switches 101 Maintenance info between source and destination switches 110 Resource management cell (for ABR congestion control) 111 Reserved PTI Meaning 0 b b Explicit Forward Congestion Indicator (EFCI) Set by Congested switch Used by AAL5 to denote end of message ATM

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Chart © Glenn W Cox, 2001-2004 End-System Address Specified by Organization Org. ID 840F

ATM Addressing

E.164: Telephone Numbers - up to 15 digits ATM End-System Addresses (AESA) -- 20-byte Addresses

39 Example Format Address Type 80 Format indicator US Code End-System Sub-address

Address Aggregation (Hierarchical Routing)

39.840F.80.809134.0001 39.840F.80.809134.0001.01 39.840F.80.809134.0001.0F 39.840F.80.809134.0001.0F.01 39.840F.80.809134.0001.0F.02 BigCorp, Inc. Plant 1 Plant 15 Bldg 2 Bldg 1 ATM

ATM

• B

ackground

• Physical and ATM Layers

• Cells, Formats, and Addressing

• Virtual Circuits

• Switches and Media

• Interfaces

• AALs

• Applicatio

ns

ATM

Virtual Paths,

Virtual Circuits

Physical Link Virtual Path Virtual Circuit

A Link can Carry Multiple Virtual Paths,

which can Carry Multiple Virtual Circuits

Advantage of Two-Level Approach:

A Bundle of VC’s can be switched by switching a single VP

VP 1 VP 2 VC 1 (1/1) VC 2 (1/2) VC 1 (2/1) VC 2 (2/2) Public Switching Private Switching ATM

Virtual Circuits

• Normally Unicast, but one-way Multicasting Supported

• Unidirectional, but a pair can be created with same ID

-- effectively full-duplex

• Customers can lease a VP, then allocate VC’s within it

(“Permanent VP”)

• Types of VC’s:

• Standard VC (“PVC”) – Static route

• Soft VC – Route can be changed in event of failure

• Signalled VC (“SVC”) – Demand connection initiated by used

ATM

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VC Connection

Messages

ATM

Message Meaning (if from host) Meaning (if from Network) SETUP Call request Incoming call CALL PROCEEDING ACK Incoming call ACK Call request CONNECT Incoming call accepted Call request accepted CONNECT ACK ACK Call request accepted ACK Incoming call accepted RELEASE Terminate request Terminate req from remote RELEASE COMPLETE ACK Terminate from remote ACK terminate request

Virtual Circuit

Setup Process

Source Host Switch 1 Switch 2 Desti-nation Host SETUP CALL PROC. SETUP

CALL PROC. SETUP CONNECT. CONNECT CONNECT CONNECT ACK CONNECT ACK CONNECT ACK RELEASE RLS COMPLETE. RELEASE

RLS COMPLETE. RELEASE RLS COMPLETE.

ATM

Switch

ATM Broadcasting

/Multicasting

Sender Dest Dest Dest Dest Cells to be Broadcast ATM

Operation Administration

and Maintenance (OA&M)

Supervison, Maintainance, Testing, Performance Measurement, Loopbacks Organized into levels according to Network Segment Type

Term

Eqpt Switch Mux Switch

Term Eqpt

F5: Virtual Channel F4: Virtual Path

F3: Transmission Path

F2: Digital Section (“Line”) F2 F1: Regeneration

Section

F1 F1 F1

Repeater Repeater

ATM

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Preassigned VPI and VCI Numbers

ATM

VPI VCI Meaning 0 0 Unassigned 0 1 Metasignaling 0 3 F4 Flow (segment) 0 4 F4 Flow (end-to-end) 0 5 Signaling 0 15 SMDS

0 16 Intermediate Layer Management Interface (ILMI)

ATM

• Background

• Physical and ATM Layers

• Cells, Formats, and Addressing

• Virtual Circuits

• Switches and Media

• Interfaces

• AALs

• Applications

ATM

Switch Operation

A 0/6 B 0/14 D 0/11 C 0/11 A 7/4 B 12/18 D 12/6 C 12/6 IN 1 2 OUT 1 2 Label Switching ATM

Switching Table IN OUT Port ID Port ID 1 0/6 1 7/4 1 0/14 2 12/18 2 0/11 2 12/6

Transmission Media

• Baseline is SONET (B-ISDN)

• Short runs, Cat 5 TP OK

• All runs point-to-point

ATM

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SONET / SDH

Payload 9 Rows 90 Columns Overhead 125 usec

Bell: Synchronous Optical Network (SONET)

CCIT: Synchronous Digital Hierarchy (SDH) Only minor differences

• Synchronous, frame-oriented, TDM • For basic SONET:

• 6480 bits/125usec = 51.84 Mbps total (“STS-1”) • User data rate =~ 50Mbps

ATM

Chart © Glenn W Cox, 2001-2004 STS-3 ST S-3

SONET Multiplexing

T1 T1 T1 • • • T1 T1 T1 • • • T3 ST S-1 STS-1 ST S-1 STS-12 Electro-Optical Conversion OC-12 ATM

STS-3 STS-3

SONET/SDH Data Rates

Electrical Optical Optical Gross User SONET SDH Data Rate

STS-1 OC-1 51.84 49.5 STS-3 OC-3 STM-1 155.52 148.6 STS-9 OC-9 STM-3 466.56 445.8 STS-12 OC-12 STM-4 622.08 594.4 STS-18 OC-18 STM-6 933.12 891.6 STS-24 OC-24 STM-8 1244.16 1188.9 STS-36 OC-36 STM-12 1866.24 1783.3 STS-48 OC-48 STM-16 2488.32 2377.7 # STS-1

Mux’ed “OC-x” means multiple users, muxed “OC-xc” means one user – slightly higher User B/W

ATM

ATM over SONET

• ATM designed to run over SONET OC-3c

• Basic: 155.52 Mbps gross rate

• Usually quoted as 155 Mbps

• New generation runs at OC-12 (622 Mbps),

OC-48 (2.4 Gbps)

ATM

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ATM

• Background

• Physical and ATM Layers

• Cells, Formats, and Addressing

• Virtual Circuits

• Switches and Media

• Interfaces

• AALs

• Applications

ATM

Chart © Glenn W Cox, 2001-2004 DXI

ATM Interfaces

Public Switch Public Carrier A Public Carrier B Public Switch B-ICI Public NNI Private Switch Private Switch Private NNI Public Switch Public UNI Private UNI Private UNI Digital Service Unit Public UNI Router ATM

Broadband

Inter-Carrier Interface (B-ICI)

• Public Network-to-Network Interface

• Based on Broadband ISDN User-Part

(B-ISUP) messages

ATM

NNI

• Switch-to-switch interface protocol

• Two versions: Public and private (similar,

more flexibility in private version)

• NNI Includes:

• Routing protocol (Link-sate/OSPF)

• Signaling protocol for link setup/teardown

ATM

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UNI

• Protocol for interfacing with user equipment

• Follows ITU-T Q.2931 message format

ATM

DXI

“Frames In, Cells Out”

Provides Frame-Based Access to an ATM Network

Non-ATM Router

HSSI, eg _ATM

Network ATM DSU ATM Cells

PHY DXI PHY

ATM UNI PHY ATM DXI AAL5 SAR AAL5 CS ATM UNI ATM

DXI Variants

Mode 1a 1b 2 AAL5 AALs Supported AAL5 AAL3/4 AAL3/4,5 VCs Supported 1023 1023 1 16.6M

Flag Header Body FCS Flag

1 2 0-9232 2 1

1 2 0-9224 2 1

1 2 0-65535 4 1

ATM

• Background

• Physical and ATM Layers

• AALs

• AAL Overview

• AAL 1 and 2

• AAL 3/4

• AAL 5

• Applications

ATM - AAL Layer

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Why AAL?

An “impedance matcher”

between ATM and

higher-level protocols

with variable-length cells

ATM - AAL Layer

The Evolution Of the AAL’s

Original Service Classes A Real time

Constant Bit Rate Connection-Oriented B Real-time

Variable Bit Rate Connection-Oriented C Non-real-time

Variable Bit Rate Connection Oriented D Non-real-time

Variable Bit Rate Connectionless AAL1 AAL2 AAL3 AAL4 AAL3/4 Telc om Indu s tr y Co m p u ter Indu s

try “Simple _Efficient

Adaptation Layer” AAL5 ATM - AAL Layer

Cell Formation

Application Convergence Sublayer SAR Sublayer ATM Layer Physical Layer A A L Lay er Data Data CS CS Data part 1 CS Data part 2 CS S A R S A R S A R S A R Data part 1 CS Data part 2 CS S A R S A R S A R S A R A T M A T M Original Message CS PDU SAR PDU ATM CELL ATM - AAL Layer

ATM

• Background

• Physical and ATM Layers

• AALs

• AAL Overview

• AAL 1 and 2

• AAL 3/4

• AAL 5

• Applications

ATM - AAL Layer

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AAL 1

• Designed to support Class A traffic (voice)

• Voice has good error tolerance -> No bit error

control (CRC) needed

• Sequence numbers needed to ID missing

cells

ATM - AAL Layer

AAL 1 Convergence

Sublayer

• Detects lost cells

• Detects mis-delivered (“misinserted”) cells

• Smooths incoming traffic to minimize jitter

• Breaks bit stream into 47/46-byte segments

for SAR sublayer

• Does not add headers or trailers

ATM - AAL Layer

AAL 1 SAR PDU

(non-pointer type)

• Adds sequence # with protection (checksum)

• Adds parity bit (even) over header

0 Cell Seq # Seq # Cksum p t y 47-byte payload 1 byte ATM - AAL Layer Pointer 1 Cell Seq # Seq # Cksum p t y 46-byte payload

AAL1 SAR PDU

(Pointer Type)

2 bytes

• Pointer field gives offset to start of next

message (0-92 bytes)

ATM - AAL Layer

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AAL 2

• Designed to support Variable Bit Rate

(“Bandwidth on Demand”)

• Provides for partial payloads to support

low-rate data with low latency

• Error protection over full PDU

• Simple flag to indicate position in message

ATM - AAL Layer

AAL2 SAR PDU

Cell Seq # Info Type 1 byte Payload Length 2 bytes CRC 45-byte payload First, Intermediate, Last ATM - AAL Layer

ATM

• Background

• Physical and ATM Layers

• AALs

• AAL Overview

• AAL 1 and 2

• AAL 3/4

• AAL 5

• Applications

ATM - AAL Layer

AAL 3/4

• Originally 2 separate AALs:

– AAL3: Connection-oriented packet svcs (X.25)

– AAL4: Connectionless svcs (IP)

• Eventually combined into a single type for all

data service

• Data support overtaken by AAL5

ATM - AAL Layer

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AAL3/4 CS PDU

Payload BA Size

Btag

CPI Pad Etag Length

1 1 2 1 to 65535 0 to 3 1 1 2

CPI - Common Part Indicator Message type, Units for BA Size and Length

Btag, Etag Identical sentinel bytes, Incremented for each new message BA Size Estimated payload size (for buffer allocation) Pad Bytes added to to make Payload a multiple of 4 bytes Length True payload size

bytes

ATM - AAL Layer

AAL3/4 SAR PDU

CRC Payload Length Cell Seq #

ST Muxing ID

ST - Segment Type Indicates if this cell is from the middle (00), end (01) or beginning (10) of this message or if this is a single-cell message (11)

Muxing ID ID of the session that this cell belongs to (the CS may be handling multiple sessions simultaneously

ATM - AAL Layer 44-byte payload

ATM

• Background

• Physical and ATM Layers

• AALs

• AAL Overview

• AAL 1 and 2

• AAL 3/4

• AAL 5

• Applications

ATM - AAL Layer

AAL 5

• Pushed by computer industry as a lower-overhead data format

• The idea: Instead of using some of the 48-byte cell payload for

SAR info, steal a bit from the cell to denote end of message

1000 by 1008 by Message CS PDU SAR PDU 1100 by AAL 3/4 1000 by 1008 by 1008 by AAL 5 AAL3/4: 4 bytes per message + 4 bytes per cell => 44 User Data Bytes / Cell

AAL5: 8 bytes per message => 48 User Data Bytes / Cell, 8% improvement

Efficiency:

ATM - AAL Layer

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AAL5 CS PDU

Payload Pad UU Length

1 to 65535bytes 0 to 47 1 1 2

Pad Inserted to make entire CS PDU a multiple of 48 bytes UU “User - to - User” field. Available for use by higher levels. Length Payload length, not counting padding

CRC

4

ATM - AAL Layer

AAL5 SAR

• Simply breaks CS PDU into 48-byte chunks

and passes them to ATM Layer.

• No overhead bytes added.

ATM - AAL Layer

ATM

• Background

• Physical and ATM Layers

• AALs

• Applications

• QoS

• LANE

• IP over ATM, MPOA

ATM - Applications

ATM QoS

• A (The?) Major ATM selling point vs. Best-Effort

• The idea:

– At VC setup, sender specifies level and quality of service

required, also planned traffic profile.

– While establishing VC, network attempts to allocate

resources to meet requirements.

– Requirements are agreed to or available capability is passed

back to sender.

– During transmission, network enforces traffic profile

ATM - Applications

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CBR Constant bit rate (e.g., Phone traffic) Y Y

VBR-RT Variable bit rate, Real-Time

(e.g., Interactive Compressed Video) Y Y

VBR-NRT Variable bit rate, Non-Real-Time

(e.g, Multimedia email) Y Y

ABR Available bit rate (e.g., File Xfer, email) Opt Y Y

UBR Unspecified bit rate (e.g., TCP/IP) Y

ATM Classes of Service

Class Description PC R -P e a k C e ll Rat e SCR -S us ta ine d Ce ll R a te BT -B u rst T o leran ce Flow C ont ro l CL R-Cel l L o s s R a ti o C T D -C e ll Tr a n s fe r de la y CD V -C e ll D e la y Va ri a tion Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y ATM - Applications

QoS Parameters

Parameter Meaning

PCR - Peak Cell Rate Max rate req’d

SCR - Sustained Cell Rate Avg rate req’d

MCR - Minimum Cell Rate Min acceptable rate (Used in ABR Service)

CDVT - Cell delay variation tolerance Max acceptable jitter

CLR - Cell Loss Ratio Fraction of cells lost or late

CTD - Cell Transfer Delay Delivery time (mean and max)

CDV - Cell Delay Variation Measured jitter

CER - Cell Error Rate Fraction with one or more errors

SECBR - Severely-Errored Cell Block Ratio Fraction of “M”-cell blocks with “N” or more errored cells

CMR - Cell Misinsertion Rate Fraction delivered to wrong destination

BT - Burst Tolerance Max Burst That can be sent at Peak Rate

ATM - Applications

Traffic Shaping

C e ll R a te Target Mean Max Burst

Unregulated Cell Stream

“Leaky Bucket”

Release at Regulated Cell Stream Max: Discard above

Mean ATM

- Applications

Agenda

• Background

• Physical and ATM Layers

• AALs

• Applications

• QoS

• LANE

• IP over ATM, MPOA

ATM - Applications

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LANE – The Goal

Router ATM Bridge To Make Work Like - Virtual Circuits - No (easy) Broadcast - Packet-Oriented (802) - Broadcast as a Basic Function

ATM - Applications

LANE Protocol Stack

Application IP LAN Emulation AAL5 ATM Physical LAN Emulation AAL5 ATM Physical Bridging Media Access Control Physical Application IP LAN Emulation AAL5 ATM Physical Media Access Control ATM Host LAN Host ATM-LAN Bridge

Virtual Circuit Packet

ATM - Applications

LANE -- Address Translation in

the Virtual LAN

“Who’s 192.18.4.4?”

192.18.4.1 192.18.4.2192.18.4.3 192.18.4.4

MAC Address

In 802-series LAN, the ARP protocol is used to translate Network-Layer Address (e.g., IP) to MAC address. Network address is broadcast to all possible targets, the right one responds.

The idea is to establish a VC to the host that a LAN packet would go to. We need a way to determine which host to set up the VC to.

LANE Server Software

Network ATM Address Address

Network Address ATM Address

LANE Client Software

LEC LES S W I T C H ATM

- Applications

Broadcast and

Unknown Server (BUS)

Provides Broadcast, Multicast Capability

LEC BUS LEC LEC LEC LEC Cells to be Broadcast Ea ch_L EC se_ts u p a “M ult_ica st _SE N_D V_C ” To_B U S a_{t p} ow erup ATM - Applications

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ATM

– Background

– Physical and ATM Layers

– AALs

– Applications

• QoS

• LANE

• IP over ATM, MPOA

ATM - Applications

Classical IP over ATM

• Could use LANE to implement ATM-IP

interoperability, but may be too much overhead

for large networks

• Defined by IETF (RFC 1577)

• The key is IP <-> ATM address resolution

• ATM Address Resolution Protocol (ATMARP)

• Inverse ATMARP (InATMARP)

ATM - Applications

IP over ATM

Connection Setup Process

IP Host

(Source) IP Host _(Dest)

ATM Ntwk ATMARP Server VC Bootup IP Host

ATM Ntwk ATMARP Server Initiating Send Des t IP Addr Dest ATM Add r IP Host